1. Field of the Invention
The present invention relates generally to temporary or removable protective coatings for substrates with and without any functional coatings and, more particularly, to removable protective coatings to reduce the susceptibility of substrates, like glass substrates having one or more functional coatings, to mechanical damage during processing, handling, shipping or storage.
2. Technical Considerations
Some sheet or panel shaped substrates, whether flat or curved, can have two major surfaces terminating in a peripheral edge, e.g., glass or certain plastic sheets, where at least one surface has visible light transmittance that ranges from greater than 0% to less than 100%. These types of substrates can have a functional coating deposited on one or more surfaces. For some substrates, such as mirrors, one surface of the substrate may be light transmitting, e.g., visible light transmitting, and the other surface visible light reflecting. These types of substrates can be further fabricated into other articles or products.
For instance, in the glass industry, large glass pieces, e.g., generally greater than about 4 feet (1.2 m)xc3x976 feet (1.8 m), are prepared by glass manufacturers and then shipped to fabricators to be cut into smaller pieces and incorporated into various production articles, such as architectural windows, automotive transparencies, insulated glass (IG) units, mirrors, and the like, which production articles are then shipped by the fabricator to customers. As used herein, such large substrate pieces which are further processed or cut for incorporation into smaller production articles are referred to as xe2x80x9cmanufacture substratesxe2x80x9d. The manufacture substrates may or may not include one or more functional coatings, such as solar control, conductive, antireflective and/or low emissivity coatings. Also, glass and plastic light-transmitting substrates may have one or more functional coatings that modify various physical properties, e.g., optical, thermal or mechanical properties, of the coated glass or plastic or its surface(s). In addition to plastic and glass large manufacture substrates having zero, one, or more than one functional coating, functionally coated glass pieces of any size may be shipped to a fabricator by a manufacturer.
These substrates are typically purchased and shipped in bulk, with several pieces shipped together to the fabricator. The substrate pieces may be bundled together and shipped on a wooden pallet in conventional manner well known in the glass shipping art. In addition to wooden pallets, specialized shipping containers are known. For example, U.S. Pat. Nos. 4,512,473 and 5,860,539 disclose shipping containers for transporting a plurality of sheets. These known shipping methods are quite adequate for shipping substrates without functional coatings or substrates of substantially uniform size. However, when shipping substrates with functional coatings or substrates of different sizes, a high spot or corner of one substrate may contact the surface, e.g., the functionally coated surface, of the adjacent substrate during handling, processing, shipping or storage and might damage the functional coating or scratch the adjacent substrate surface.
In some industries, protective coatings have been used in order to reduce shipping damage. For example, French reference FR 2,295,100 describes a peelable protective coating for surfaces of metals, glass and plastic. Such a peelable coating is formed from a liquid composition of 5 to 40 percent soluble copolyamide, 55 to 85 percent ethanol and 0 to 20 percent water. However, the disadvantages of such peelable coatings with a large amount of organic solvent are threefold. A large amount of organic solvent must be reclaimed, recycled, or disposed of after being used in the deposition of the peelable protective coating. Also, the solid peeled film must be properly disposed of. Further, considerable time is required to peel the coating completely off of the substrate surface. For hastily removed peelable coatings, small patches of the peelable coating may remain on the substrate, requiring increased time and labor costs to inspect and remove these small patches. Additionally, some organic solvents may be flammable.
Other types of temporary protective coatings used in various industries are typically formed from polymers or waxes applied and, after shipping, removed with polar and/or non-polar solvents, e.g., organic and/or inorganic solvents, such as acidic or alkaline solvents, hydrocarbons or lower monohydric alcohols. For example, see JP 7567845 where alkaline inorganic cleaning solvents remove a polymeric shipping coating. Such an approach still has the drawback of the need for disposal of corrosive or caustic solvents and/or inorganic salts, which requires that the accumulating wastewater be treated or neutralized. Further, alkaline or acidic solvents may be incompatible with certain substrates or any functional coatings present on the surface of those substrates. Additionally, for plastic substrates, certain organic solvents may discolor, stain, oxidize or swell the substrate or make the substrate more brittle.
U.S. Pat. No. 4,315,947 (equivalent to German Application No. 2926197) discloses the removal of a wax-based protective coating using a mixture of water and steam at a temperature of 90xc2x0 C.-95xc2x0 C. The steam removal process is energy intensive and poses the risk of scalding by the hot water/steam mixture.
U.S. Pat. No. 5,026,597 discloses a temporary protective coating formed from a water soluble film-forming polymer and insoluble spacer particles, such as polyethylene or acrylic beads. The spacer particles become integrated into the structure of the dried coating. No coating thicknesses are given and no mention is made of incorporating identification materials, such as colorants, into the coating.
Therefore, it would be advantageous to provide a method of forming a removable protective coating over a substrate with or without one or more functional coatings, particularly a substrate with some visible light-transmitting characteristics like glass, which reduces or eliminates at least some of the drawbacks discussed above.
An article of the invention includes a substrate, preferably a substrate having at least one light-transmitting surface, with a removable protective coating deposited over at least a portion of the surface. The substrate may be coated with one or more functional coatings of various types. The removable protective coating is deposited over the substrate surface where protection is desired. This protection can be from mechanical, chemical or handling damage and/or from misidentification. For large size or xe2x80x9cmanufacturexe2x80x9d light-transmitting substrates on the order of greater than about 4 feet (1.2 m) by about 6 feet (1.8 m), the protective coating is preferably deposited over most, preferably all, of the exposed substrate that might not be protected by some form of packaging, such as corners, frames, or edge guards. For substrates with at least two major surfaces, one or more of the surfaces (e.g., a first surface) can be coated with the protective coating. For substrates with one or more functional coatings, (e.g., a functional coating on the first surface) the protective coating is preferably deposited over at least a portion of the functional coating(s) to protect the functional coating(s) from mechanical and/or chemical damage and/or misidentification during shipment, storage, handling, and processing. The functional coating may be a single layer or a multiple layer coating, and may include one or more metals, non-metals, semi-metals, semiconductors, or alloys, compounds, composites, combinations, or blends thereof.
In one aspect of the invention, the protective coating results from the evaporation or reaction product of a polymeric coating composition, e.g., a liquid solution, emulsion, suspension, slurry, or dispersion, deposited over the substrate. For substrates without functional coatings or with just a single layer metal oxide coating, the coating composition may be essentially free of spacer material. The protective coating can be subsequently removed by washing with an appropriate solvent or by combustion or thermal decomposition.
In another aspect of the invention, the protective coating is a substantially carbon coating applied over the substrate, for example by conventional chemical or vapor deposition techniques or methods. This substantially carbon protective coating may be subsequently removed by combustion.
Another aspect of the invention includes a method of identifying selected substrates. The method includes forming a removable protective coating of a different selected color, texture, pattern, appearance, scent or otherwise discernible identifying property on different substrates to distinguish the different substrates from each other. The removable protective coating may be formed by applying a coating composition e.g., solution, emulsion, suspension, slurry or dispersion, over at least a portion of the substrate. The coating composition may then be cured or dried, to form a protective coating of a selected or desired appearance, color or scent over the substrate. The protective coating may subsequently be removed by an appropriate solvent or by combustion or thermal decomposition.
In a further aspect of the invention, a coated article is provided which includes a flat glass substrate having a first surface and a removable protective coating deposited over at least a portion of the first surface. The protective coating has a thickness of less than about 50 microns and is deposited from a coating composition that is essentially free of spacer material.
An additional aspect of the invention is a method of preparing a shipping container of flat or curved sheets, each having a first surface. A removable protective coating is applied over at least a portion of the first surface of at least a portion of the substrates. The substrates are arranged in the shipping container such that at least one protective coating is located between at least one pair of adjacent substrates.
Another aspect of the invention is a method of fabricating an article which includes receiving a shipping container, the shipping container having a plurality of substrates, with each substrate having a first surface with a removable protective coating located on the first surface of at least a portion of the substrates and with the substrates positioned such that at least one protective coating is located between at least one adjacent pair of substrates. The protective coating is then removed from at least one of the substrates, e.g., by washing, combustion, or thermal decomposition. The substrate can be processed, e.g., cut, trimmed, bent, shaped, and/or incorporated into a production article, before or after removal of the protective coating. Another removable protective coating, which may be the same or different from that discussed above, can be applied to at least a portion of the production article before shipping or handling the production article.
A still further aspect of the invention is a method of promoting uniform heating, e.g., tempering, bending, shaping, or heat-strengthening, of a substrate having a functional coating, such as a low emissivity or solar control coating. The method includes applying a removable, high emissivity coating over at least a portion of the functionally coated substrate before heating. The high emissivity coating provides increased heat absorption compared to the functional coating and, hence, decreases the time required to heat the substrate to a desired treatment temperature. The high emissivity coating is configured to combust or thermally decompose during the heating process.